The invention relates generally to the field of marine electromagnetic geophysical surveying apparatus. More specifically, the invention relates to electrode structures for marine electromagnetic geophysical survey transducers and methods for making such electrode structures.
Marine electromagnetic geophysical surveying is used to infer spatial distribution of electrical conductivity below the bottom of a body of water such as a lake or ocean. The spatial distribution of conductivity is used to assist determining presence of hydrocarbon bearing formations in the subsurface. One type of such surveying is known as “controlled source” electromagnetic surveying, and generally includes inducing a time varying electromagnetic field in the subsurface formations and measuring one or more parameters related to a response of the subsurface rock formations to the induced electromagnetic field.
Devices for inducing such electromagnetic fields are generally referred to as “sources” or “transmitters” and include, among other devices, spaced apart electrodes disposed along or at the ends of a cable. The cable may be towed by a vessel in the body of water. Time varying electric current is imparted across the electrodes to induce a time varying electromagnetic field in the water and subsequently in the subsurface formations. Structures typically used for the electrodes include metal cylinders or tubes. Such cylinders or tubes may be suspended at a selected depth in the water by the use of floatation devices such as buoys. Such electrode structures have respective deployment and maintenance procedures.
There is a need for improved structures for marine electromagnetic geophysical survey transducers and electrode structures used with such transducers, as well as methods for making the electrode structures.